Before
the 15th century, western music was written by hand and preserved
in manuscripts, usually bound in large volumes. The best known examples
of these are medieval manuscripts of monophonic chant. In the case
of medieval polyphony, such as the motet, the parts were written
in separate portions of facing pages. This process was aided by
the advent of mensural notation to clarify rhythm and was paralleled
by the medieval practice of composing parts of polyphony sequentially,
rather than simultaneously as in later times. Manuscripts showing
parts together in score format were rare, and limited mostly to
organum, especially that of the Notre Dame school.

Even
after the advent of music printing, much music continued to exist
solely in manuscripts well into the 18th century.